EASTHAMPTON — Last month, less than a month after Police Chief Bruce W. McMahon had knee surgery following a bad fall, he was back at the hospital for a life-threatening complication. He suffered a pulmonary embolism when blood clots from his healing knee traveled to his lungs and nearly killed him, he said Tuesday.

“It was very scary. The doctor said with that size clot, only about 10 percent survive,” McMahon said at the Public Safety Complex, where he was back on the job on a part-time schedule Monday. “He said, ‘You’re lucky — you should play the lottery.’ ”

McMahon said he feels fortunate that his lungs were not damaged and he is expected to make a full recovery, but admitted “it hasn’t been a good year” for him. He probably won’t be able to resume his full duties until May.

On Jan. 1, the 53-year-old was off-duty when he slipped on ice while walking in a friend’s driveway in Southampton. The fall dislocated his knee cap and severed his patella tendon. He had surgery to repair it and two weeks later was back at work on a reduced schedule at the Public Safety Complex, getting around on crutches and then a cane.

But on Jan. 29 he fainted at his home and couldn’t breathe, so he was rushed to a hospital. Doctors diagnosed him with a pulmonary embolism and dissolved the clot with medication. He was in the critical care unit for three days while his lungs returned to good working order. He was released after five days, but he said at first he couldn’t walk 40 feet without needing to rest.

Pulmonary embolisms occur when a blood clot that usually develops in the legs travels through the bloodstream and causes a blockage in the lungs, sometimes stopping blood flow to the lungs completely, according to the Centers for Disease Control.

The risk of a pulmonary embolism increases dramatically if a person has surgery because it can often damage a vein, and blood flow is slowed while the recovering person is limited in movement, such as being confined to bed or a cast.

“Knee and hip surgeries pass the most clots,” McMahon said. “Two clots in my knee broke loose, passed through the heart and into the lungs. I could barely breathe.”

He said doctors found that other clots were still developing in the knee, so they surgically implanted a kind of filter into his vein that will prevent any future clots from reaching his heart or lungs. He is also on blood thinners.

His lungs are working at about 75 percent now, he said, and they should be back to 100 percent soon.

Mayor Michael A. Tautznik said the city is glad the chief is on the road to recovery.

“It was actually pretty scary and we’re happy he was able to get through it and that he’s recovering and getting his breath back,” Tautznik said. “You always worry about your help, and we really appreciate his skills and his talents and the way he leads the department.”

Meanwhile, McMahon’s knee is healing well in a large brace that runs nearly from hip to ankle, keeping his right leg straight.

“Tomorrow I go to the surgeon to get this big brace off and get a smaller brace, and then I can start physical therapy,” he said. “They said I’ll probably be back to normal by May.”

McMahon said that in addition to his half days at the Public Safety Complex, he is working some from home and taking some sick time. Sgt. Christopher Patenode is in charge when he is home.